Television transmitting device



Filed sept. 29, 1934 N w@ E E Tw ,L 'A/FM V f E J UNM N6, N P I E M E 0 i T .V T T M m 4 m, Wm A (m LN mm NCU @Fw AV v Oct. 14, 1941.y

VEET/CHL DEF/.ECTION G/E'cL//T o Patented Oct. 14, 14941 mesne assignments; to Radio VCorporation of A`America; New Yorin 51N. Y.; a corporation Iof Aplcauo semanita 29, isgseral Np. 746.094

23 Claims.

My invention relates tor improvements in television transmitting devices. n In the development of picture signals for television transmission, a cathode'ray tube has been used for scanning. Y One type of such a tube is provided at one end thereof With almosaic, photosensitive screen, and at its other end with a gun for developinga ray of electrons and directing the ray at the screen. The ray isfocused on the rscreen andy isvdeflected horizontally and vertically ysimultaneously to scan the photofsensitvesurface of. theV screenupon which an optical imageof the object or subject for transmission is projected. f

An important characteristic of operation in the v-.transmitting tube of the type referred .to resides in the fact thatfrcm vthe operating surface c `f"the'sc1eenr thereoccurs both the-,emission of photo-electrons due to light from the object and the emission of secondary electrons due to bombardment of lthis ysurface byY the high velocity electronsin the scanning ray. The eniciency of these tubes-is not as high as it is. believedfpossible.; This isdue, it'seems,r tothe fact that the photo-sensitivity,-oraction of the pho-VV to-electrons leaving vthe yoperating surface; is interfered with-by the secondaryN emission, or action of electrons leaving .the operating` surface 'due to bombardment thereof` by the electronsyof thescanningray. f. Furthermore, in these tubes, diiiculties are encountered in making the screen which is comprised of. a sheet of insulating materiahsuchvas mica' provided on one side thereof with. a coating of silver, and on its other sidewitha large number of minute silver g-lobulesf or elements each insulated from theothersand each .photosensitized. .While these screens have been .made

Without particular diiiiculty up to the pointv Where the insulating sheet. has been -providedfwith the silvercoating on one side and the minute silver globules on-the othersidei difficultyhas been. eX- perienced when the-next step of photosensitization is carried out. That is, there has been the difliculty of obtaining uniformity of photosensitization over the surface, and Vof n preventing at least some degree of leakage between adjacent elementsof the mosaic surface due to deposition of photosensitive material in the almost microscopic spaces between the adjacent silver globules. f

v Furthermore, in the-tubes referredto above, the degree of photosensitivity obtainable is lim- 1iteddueto the fact that it has not been. feasible jected. The tubeis provided vat to apply a polarizing potential tothe sereen;.lfor the purpose of increasing' the .photo-'emissioni With the foregoing in-m'nd,`.it isfone'bflthe objects of my invention to 'provide va'iijirnprb'izecl television transmitting fdevicepf. the character referred to inwhich`the action ofemissionff photo-electrons is independent. ofthe act'ionfof emission of secondaryelectrons, andin'iwhicl'iit is possible to apply ajg'ola'rizing potential Y to-the photo-sensitive surface 'to' obtain' a' 4degree.fof photo-electricY sensitivityY substantially. -,gre`atr than has been possible under thefsaineV conditions with the various."transmittingjtubes prol'os'ed heretofore. Y v Other objects "and advantages will her appear. n 1 lnaccordance Withiny'inventiomI prfo d a tube at one end thereof .withfaf screenhavinga continuous layer of photo-sensitive lmaterial upon which an optical image of the objectispi'oits, other;A end with a screen having overa surfacethereofga mosaic comprised of a great number of `,minute metallic elements each insulated from y.the others. 1n operation, 'photo-electrons leavev the; .surface `of the" rstscreen under` the.inuence; oflight from'the objectand .also-under.' the influencegfa polarizing potential applied- ,to an .adjacentfgrdl' In' this Way, thev photo-electrons,leaving.anti

particular 'elemental area of the .rst screen re, under the influencebf `a .focusing rfleld, ca to travelto the second screen and to causes age on the corresponding elemental area the of* of -an electrostatic charge lwhich is neutralized by the cathode ray during. the scanningf actiomkto develop the picture signals.`

My invention resides in the improved tion and method of operation of thecharacter hereinafter described and claimed..

For the purpose of illustratingmyinvention, an embodiment thereof is shown in-thejdrawing, wherein A 'g Figure 1 is a diagrammatic view of a tele, transmitting system..embodying a;jtransmitting` `device constructed and operating in ,aceordarce' with my invention frto develonpicture signals;W

. Figs- 2 andf3fare detail,`fragmentarymectinal views, taken from Fig. L1;

' Fig. 4 isfa diagrammatid-fragmentaryvievv; v

illustrative of a modiicationof the i devicegin Y Fig. 5 is a view similar to 1Q sho modificatiomande Lf'. Fig. 6 is' ajdetail, fragmentar/Svtona vie i, taken from Fig.'5'.1-- l ion Y With reference to Fig. l, I designates a tube provided at one end thereof with a screen I2 and at its other end with a screen I4.

The screen I2 comprises an imperforate metal plate I6 provided on a surface thereof with a substantially continuous layer I8 of photosensitive material such as caesium.

The screen I4 comprises a sheet 20 of mica or other insulating material provided on one side thereof with a coating 22 of metal such as silver, and on its other side with a mosaic surface 24 comprised of a great number of minute metallic globules or elements 24a. i practically microscopic in size, and; are spacedA from and insulated from each other by the mica.

As shown in the drawing, the .screens I2 and I4 are disposed so that the photosens'itive surface I8 and the mosaic surface 24 face each other.

Inl operation, an optical image of theV object or subject for transmission is'projected onto the photosensitivesurfacel I8 by a lensl or optical system Z'Bdisposed with its axis 28 perpendicular to the' surface I8. In` this Way, photo-electrons` are caused to ,leave the surface i8, the degreejof photo-emission from any particular elemental area, such asx, for example, being proportionalto the light intensity at the time onthefcorresp'onding elemental area of the obje'ct.

"'Thedegree vof'photo-emission fromV any particularelementalar-ea for a given'degree" of light intensity on sucharea is increasedV substantially by a polarizing vV to a'grid'32 disposed' adjacentV to and in a' plane parallel to the photo-sensitive surface I8: `*The grijd 32 :may be in theV form'of a screen'of'ne wiremesh ora metal ring.

more positive than the potential on the screen I2, 'photolelectron's leave the surface I8 freely, and travelto' vthe screen I4 inthe f'orrnofin'- dividualrays. Each ray is focusjedjpn the mo.-

These elements ,are

Withthe grid lf'ata'4 potentialsubstantially oltage applied from a source 36 saic` surface 24 Aby a magnetic field developed by aV coil '34'dispose'd'ab'out the'tubje It.Y The electrons, up'on striking the' screen I4, cause an electrostatic charge to be` developed at the cor; responding lelemental `areaJg/,vfor example, the value," of this charge corresponding to the degree o f photoelectric emission from the correspondin'g 'elemental' area a: of the photosenjsitive surface I8. t

Since there'is photofelectric emission from each of the element'alareas overth'e surface I8, the degree "of such emission from any particular elemental area corresponding to the degree of light intensity to which it is exposed, it can b'e said that when 'an optical'image of the object is projected onto the'scre'en I2 a current image is developed'` and, under the focusing action ofthe coil 34, is utilized to develop an electrostatic image over the operating surface 24 of the screen I4.

The picture signals are 4developed by neutralizing' successively the individual electrostatic charges bound on the screen I4, for which purpose the' tube IU' is provided with an electron gun` 38 for developing a rayf'4 of'Y electrons and directing the ray at th'escreen I4. The ray 40 is deiiected horizontallyby plates 42 across which a saw-'tooth voltage wave is applied `from a suitable circuit 44, and is simultaneouslydeflected vertically by coils 46 through which a saw-tooth curr-ent wave, supplied from a 'suitable circuit 48, is caused to pass. Anan'odeVV 5j), in the form of a silver coating on the inside surface "of assegno the tube, and which is at a potential substantially more positive than the potential on the various elements comprising the gun 38, operates to focus the electron ray on the mosaic surface 24 of the screen I4 and to accelerate the electrons toward this screen.

As the ray 40 scans the screen I4, at each elemental ar-ea of the surface 24 the electrostatic charge previously bound at this point is neutralized, and electrons of secondary emission are emitted from this point and permitted to pass to-grou'nd by way of the anode 50.

During the scanning action the difference betweenu the degrees of secondary emission from any'two elemental areas correspond to the difference between the respective electrostatic charges previously stored at these two elemental areas. Picture signals are developed in a conn-ection, 52, leading to a suitable amplifier and transmitter 54 from the metallic coating 22 which constitutes, with each of the metal elements 24a on the opposite surface of the mica sheet 29', a minute condenser.

The tube itself is under a high vacuum, and the wall thereof is transparent to permit theentrance of light to the screen I 2.

As represented in the drawing, the screen I2 is maintained at a relatively high negative potential with respect to ground.

From the foregoing it will be seen that I have provided an improved construction of television transmitting device embodying a mosaic screen', andinwhich the emission of photo-electrons takes place separately and independently from the Vemission of secondary electrons incident to scanning action by the cathode ray. On account of the novel combination and arrangement in my improved construction, it is feasible to employ means such as the grid 32 for the purpose of applying a relatively high polarizing potential to the screen from which photo-electric emission takes place. Furthermore, in my improved ccnstruction, it is not required that the'mosaic surface 24 be photosensitized for the reason that the satisfactory development of picture signals does not depend necessarily upon any action of photo-electric emission from this surface. In this way, the requirement for photosensitization of the mosaic surface, with the accompanying possibility of occurring leakage paths between the adjacent minute particles of the mosaic, is avoided.

If it occurs that, in a particular construction embodying my invention, an excessive and undesirable amount of electrons from the screen I2 reach the screen I4, it is proposed to remove these by making the individual elements 24a of the mosaic surface 24 photosensitive, and project onto this surfacea steady, uniform light from a source'represented at 55 in Fig. 4. Y

In the modification shown in Fig. 5, the electron gun 38 is disposed-on the side of thescreen I4 opposite that'to which the photosensitive sur-- face I8 of the screen I2 is directed. In this construction, the screen |40., correspondingto the screen I4 in Fig. 1, is'comprised of a metallic plate 22a, corresponding to the metallic coating 22 in Fig' 3, and provided with a large number of rminute apertures in which are disposed metallic elements or inserts 24h. corresponding tothe elements 24a, in Fig. 3. Eachof the elements 24bgis insulatedv fromV the plate 22a by an insulating sleeve or coating 29a corresponding lto and serving the same purpose as the mica sheet 2li in :2,258,728 Fig; 3 wherebyithe plate 22a' forms,` with each of the elements 24h, a minute condenser.

i VI'n'operatiomthe photo-electric emission from thenscreen. l2 vcauses development.;A of individual electrostatic chargesonA the screen Ida. Thesev charges are neutralized successively as the cathodefray 40 scans Athe right-hand surface of thev screen..v Electrons of secondary emission are emitted from this surfaceand pass to ground by'wayfof. the second -ahode 59a corresponding; toyand'serving'thessamez purpose as the anode 50 finvFig. 1. q

Theconstruction and operating action in Fig. is otherwise the samev as in Fig. 1.

vIt will `be understood that various modifications, within the conception of those skilled in the art, are possible withoutdeparting from the,- spirit ofmy invention orv the scope of the',claims.`

v*Iclaim as my invention. Y t, 1. A 4television transmittingdevice comprising a tube,= an `imperforate screen disposed withinv said'tub'e and'providedwith a continuous photosensitive surface, asecond screendisposed within Asaid tube and provided with'a mosaic surface, meansfor projecting onto said continuous photosensitive surface an optical image of the subject for vtransmission whereby' photo-electrons are caused to-be emitted from said surface, means for causing the electronsfemitted to travel toward andto become focused -upon said mosaic surface, means within the tube for developing a ray of electronsfand directingthe same at said secondscreen, and meansfor deflecting said ray to cause the same to scan said second screen.

2. Atelevision ltransmitting device comprising a tube, an imperforate screen disposed within said tube--and provided With'a substantially continue ous photosensitivesurface; a second screen disposed Within said tube and vrprovided with a mosaic surf-ace comprised of individual elements insulated from each other,y means for projecting onto said photosensitive surface an optical image of the subject for transmission wherebyphoto-- electrons are caused to beg'emitted from said surface, means vfor causing the emittedelectrons to travel -towardsaidmosaic surface, means for focusing `the photo-electrons issuing from said photosensitive surface with respect to said mosaic surface,means within the tube for developing a ray of electrons and means directing the same atsaid; second screen, `and means for deflectingV saidvrayto cause the same to scan said second screen- V .V i; c A Y 3.vv A television transmitting device comprising aftube, a iirst screen disposed Within said tube and provided with a photosensitive surface','a sec.Y ond screen disposed within said tubeV and arl ranged to receive Apl'1oto-elec`trons issuing from said surface, an accelerative Velectrode disposed within said tube in proximity to said surface and capable of holding a potential substantially more psitive than the potential of said first screen, means for projecting onto said photosensitive surface an optical image of the subject for transmission to cause emission of photo-electronsfrom said surface, anelectron lens means for focusing the electrons released. from the first sceen upon the second screen means within the tube for developing a ray of electronsand means for directing the same at said second screen,V and means4 fordeflecting said ray to cause the sameto vscan said second screen. 'Y

, 4. A television 'transmittingdevice comprising atube, a first screen disposed Within said'tube vnvdlrrovided with a photosensitive surface, a

z positioned within the tube envelope andadapted second screen disposed within said-tubeand Vpro-y vided with a mosaic surface Vfacing and sl'lbstanef tially parallel to said photosensitive,surface,v anY optical system for projecting onto-said ,pllIQtQ-fY sensitive surface an optical image of thesubjectf for transmission whereby photo-electrons' are, caused to be emitted from said surface, means :forg causing the photoelectrons to travel toY saidA mosaic surface, means for developing an electri-`Vl cal fieldto focus the photo-electrons on said mo'-- saic surface, means within said tube for, develop-` ing a ray of electrons and means for directing'` the produced ray at said mosaic surface, and. means for deecting said ray to causethe same tuscan said mosaic surface.

5. A television transmitting device comprising a tube, a first screen disposed within said tube and l provided With a photosensitive surface, v'means within said tube for developing a ray of electrons,

- a secondscreen disposed within said tube between]V said means and. -said first screen,V saidf-second.; screen being provided with a mosaic of individual elements, means for projecting onto said-pho?t tosensitive surface an optical image yof `thesub-y ject for transmission whereby photo-electronsarecaused to be emitted from said surface, meansff for-causing the photo-electrons ,to travel to, said-l,` second screen to develop individual electricstatieL charges upon the isolated elements :comprising: the mosaic, an electron lensmeans forv focusing.` the electrons released fromthe `first screen-.by light impinging thereon to spatially relatedareas.r of the mosaic and'omeans for deflectingsaid rayr to cause the same to scan said secondjscreen.

, 6. A methodof transmitting television signals which comprises producing an electronic `currentl image of a subject, focussing` the electronsof thecurrent image upon a mosaic electrode surface` to develop thereupon an electrostatic replica of. the current image, and `scanning the Velectrostatic,V replica to produce signals representative ofA the subject initiating the current-image.

v7. The method ofproducing television signals l which comprises producing an electronic current image of a subject, accelerating the r electrons of.,

the current image in the direction of afrnosaic' electrode, focussing the acceleratedr electron forming the current image upon the mosaic elec? trode to develop thereupon an electrostatic Arep-f lica-of the current image, producing a` cathodef: ray scanning beam, and scanning the `mos`aic, electrode with the produced cathode ray .beam f 8. A television transmitting tube compr an envelope, a continuous photo-electric sur to release electrons under the influence of light. a mosaic photo-electric surface also positioned within the envelope and supported to receive the' electrons released from the continuous photo-1' lelectric surface, and means for vdeveloping A'afi' electron beam adaptedto scan the mosaic surface" upon which the electrons from the continilolsv photo-electric surface impinge.

9. A television system comprising an electron`4= tube having in one end thereof amosaic, elec--` trode, a continuous photo-electric Velectrode and an electron gun positioned of the tube and each adapted to direct 'electrons' toward the vmosaic electrode, meansfor i1luminat* ing the continuous photo-electric-surface to cause electrons therefrom to be released .toward the mosaic electrode, and means'for causing the elec-z trons from the cathode ray beam developed from f the'electron gun to sweep the mosaic electrode1 for 'scanning and producingnsignals.

in the opposite end f In a picture transmitting device, a photoelectric plate, meansfor forming an optical imagel thereon to form an` electron image of the object,

an4 anode for attracting the electrons formingV the image, an electron lens for focusing the electron image in a plane spaced from the photoelectric plate, a memberin saidplane composed of av conductor entirely covered with insulating'v material and having an electron storage member plate, means for casting-an optical image thereon to form an electron image of the object, an electron image storage means, means for causing the electrons from the photoelectric plate to move towards the storagermeans, an electron lens for forming an electron image of the optical image on the storage means, an electron gun and means for causing the cathode ray beam from the electron gun to scan the storage means to remove theelectron image therefrom and to successively develop electric signals proportional to the tone value of successive points on the optical image.

12; In apparatus for transmitting images which comprises a photo-electrically active screen upon which a light image is adaptedV to be directed to release photo-electrons and a mosaic electrode formed from a multiplicity of mutually insulated elements adapted to be scanned for transmission by a cathode ray beam, the method which comprises the steps of projecting an optical image upon the photo-electric screen to release photoelectrons, accelerating the released photo-electrons toward the mosaic electrode, focussing the accelerated` electrons in their path toward the mosaic electrode, traversing the mosaic electrode with the cathode ray beam, and releasing electrical signaling impulses in` accordance with the intensity of the initially released photo-electron flow.

13. A scanning device comprising a mosaic electrode of elemental condensers, a photoelectric cathode, an electron lens intermediate the mosaic and photoelectric cathode, a thermionic source of electrons, and an Velectron ray focusing system intermediate the thermionicsource of electrons and the mosaic. t

14A scanning device comprising a mosaic electrode of elementalcondensers, a photoelectric cathode, an electron lens intermediate the mosaic and `photoelectricV cathode, a thermionic source of electrons, an electron ray focusingsystem intermediate the thermionic sourceof electrons and the mosaic, and an electron ray deflecting system symmetrically disposed about the focusing system.

15.,An electron discharge tube comprising a photoelectric cathode, a mosaic electrode of elemental'v condenser elements having secondary electron emissive properties, means to project electrons released from the photo-electric cathode` upon the mosaic, focus` the photo electron stream upon the mosaic, means` for scanning ment. by a focused beam, of electrons,V andv means tocollect secondary electrons ejected from the, elemental condenser ,elements produfledv by, the,

an electron lens means tothe mosaic element by eleimpact of the projected focused beam of electrons.

16,-An electron discharge device, comprising a mosaic electrode of elemental condenser ele-V ments having secondary electron emissive properties, photo-electric means for projecting an electron image upon the mosaic electrode, an electron lens means to focus the projected electron image upon the mosaic electrode, means to scan the mosaic element by element by a focused beam of electrons whereby secondary electrons are ejected in accordance with the elemental density of the electron image, and means to collect the emitted secondary electrons.

17. In the method of transmitting images of anobject to a distance wherein there is provided a photoelectrically active screen and a mosaic screen formed of a plurality of mutually insulated elements, the steps of projecting an optical image of said object upon the photoelectrically active screen to generate photoelectrons therefrom, accelerating the generated photoelectrons toward the mosaic screen, focusing the accelerated photoelectrons upon the mosaic screen, regulating the velocity of the photoelectrons to emit from the mosaic screen secondary electrons less in number than the incident photoelectrons whereby each element acquires a negative charge, scanning the mosaic screen With a primary beam of electrons to bring the potential of each element in turn to a more positive value substantially the same for each element, and transmitting signals derived froml the changes of potentials of said elements.

18. The method according to claim 17 comprising in addition the step of projecting the beam of primary electrons upon the side of the mosaic screen facing the photoelectrically active screen.

19. The method according to claim 17 comprising in addition the step of projecting the beam of primary electrons upon the side of the mosaic screen facing away from the photo-electrically active screen.'

20; In the method oftransrnitting images of an object to a distance wherein is provided a transparent photoelectrically active screen and a mosaic screen formed of a plurality of mutually insulated elements, the steps of projecting an optical the photoelectrons to emit from the mosaic screen secondary electrons less in number `than the incident photoelectrons, whereby each element ac from, means for accelerating the generated electrons toward the mosaic screen, means for focusing the accelerated photo-electrons upon themosaic screen, means for regulating the velocity of the photoelectrons to emit image of the object upon one side of the transparent screen, accelerating photoelectrons emitted from the other side of the screentowardthe mosaic, focusing the emittedy photoelectrons upon the mosaic screen, regulating the velocity ofbeam of electrons to bringl from the mosaicV screen secondary electrons less in number than the incident photoelectrons -Whereby each element acquires a negative charge, means for scanning the mosaic screen with a primary beam of electrons to bring the. potential of each element in turn to a more positive value substantially the same for each element, and means for transmitting signals derived from the changes of potentials of said elements.

22. An electro-optical transmitting system comprising a photoelectrically active screen, a mosaic comprising a plurality of mutually insulated elements, means for projecting an optical image of the object upon one side of the transparent screen, means for accelerating photoelectrons emitted from ythe other side of the screen toward the mosaic, means for `focusing the emitted photoelectrons. upon the mosaic screen, means for regulating the velocity 0f the photoelectrons to emit from the mosaic screen second- 20 ary electrons less in number than the incident photoelectrons, whereby each element acquires a negative charge, means for scanning the mosaic screen with a primary beam of electrons to bring the potential of each of the elements of the mosaic screen sequentially to a more positive value substantially the same for each element, and means for transmitting signals derived from the changes of potential of said elements.

23. In a television transmitter a cathode ray tube including a photosensitive screen at one endJ a second screen of imperforate insulating material spaced from said rst screen, means intermediate said screens Afor causing electrons emitted from said photosensitive screen to travel to said second screen and means including a cathode ray gun structure for scanning said second screen with an electron beamv to develop y picture signals.

ALDA V. BEDFORD. 

